What is a colonoscopy?

A colonoscopy is a procedure during which a flexible tube, known as a colonoscope, is inserted into the anus and through the rectum so it can view the inside of the large bowel (the colon). This tube transmits images to a screen where signs of a medical condition can be seen.

The colonoscope is about half the thickness of an electrical cord. It has a camera and light so that the bowel can be viewed in detail.

It is flexible and can be turned around curves, allowing it to travel through the length of the colon.

When is a colonoscopy recommended?

A colonoscopy may be recommended in order to investigate unexplained changes in bowel habits.

People usually have a colonoscopy:

  • to identify the cause of gut-related problems such as abdominal pain or bleeding from the anus
  • if they have had a positive bowel cancer screening test (poo test)
  • if they have a high risk of illness due to chronic bowel disease or a family history of bowel disease such as bowel cancer
  • to identify the cause of unexplained weight loss
  • following a recommendation from a previous colonoscopy

When should I have a colonoscopy as a screening test?

A colonoscopy is the best way to diagnose and prevent bowel cancer and for most people it is a straightforward test. However, as with most medical tests, complications may occur.

How do I prepare for a colonoscopy?

Bowel preparation is not pleasant but essential for an accurate and safe colonoscopy. If you need to have this procedure, you will be given detailed instructions on each stage of the bowel preparation which will take into account your individual needs.

A complete bowel preparation involves:

  • modifying your diet — this may start several days before your colonoscopy and you will have clear instructions on what you can and cannot eat
  • taking a bowel preparation (a strong laxative) — your specialist will recommend the right one for you
  • increasing your fluid intake — you will be given specific instructions on the type and amount of fluids to have leading up to your examination

The bowel preparation will cause diarrhea so it should be done while at home with easy access to the toilet.

The area around the anus may become irritated by diarrhea. Showering, and using moist wipes instead of toilet paper, may ease this discomfort.

It is important to drink only clear fluids on the day before, and to not eat solid foods or dairy products like milk.

You might have some minor side effects from the bowel preparation, including:

  • nausea
  • bloating
  • abdominal distension

If you experience any minor side effects take a short break and then start taking the bowel preparation again.

More serious side effects include:

  • dizziness
  • fever
  • severe headache

The more serious side effects might indicate dehydration or an allergic reaction to the bowel preparation. Contact your doctor if you have any serious side effects or if you can not finish the bowel preparation.

If you take regular medicines, talk to your doctor well before you start taking the bowel preparation. Some medicines should be taken as normal, and some can be delayed. It is particularly important to talk to your doctor if you take blood-thinning medicines.

What happens during the procedure and straight after?

The colonoscopy lasts for between 25–45 minutes. Most people have a mild anaesthetic or sedation to minimise any pain or discomfort. The sedation also means you may remember nothing or very little of the procedure.

During the procedure

You will be positioned on your left side and given sedation before the colonoscope is passed into the colon. The colonoscope is inserted at the end of the large intestine and then withdrawn slowly so the lining of the colon can be examined again.

Air is also pumped into the colon to help the doctor examine the lining carefully. During the procedure, polyps (small tissue growths that might develop into cancer) may be removed and small tissue samples (biopsies) may be taken and sent to the laboratory to determine what type of disease is present.

The procedure is usually performed as day surgery and you will be monitored in recovery for an hour or two after the procedure until the sedation wears off.